How Much Difference Does a More Powerful Amp Make?

Isn't that what the Pass "first watt" thing is all about? There are a hundred things that make up a great amp, and power is only one of them. I think 100 clean high gain watts per side is just about right for my rig and room, but I was at a friend's place recently and he had some little triode tube mini watt thing and it sounded amazing, although not very loud. Note that for live stuff I've always used VERY large wattage amps...350 watts minimum into each speaker or uncompressed things don't fare well.

But there are some very good high powered amps that compete with and beat their lower powered siblings, like the Mccormack DNA 500. But it's always about synergy with your speakers and using the power that THEY need, not that your ego needs.

The first Watt of a more powerful amplifier need not be worse than the first Watt of a less powerful amplifier. Furthermore, a more powerful amplifier can often provide better power longer than a lower powered amplifier, even though it hasn't exceeded the total power output of the lower powered amplifier.

Definitely maybe. Speaking as one without the technical experience to even provide you with an opinion...at all costs audition in your system compared to your current component.

That said, I heard the Sanders Magtech amplifier in a somewhat familiar system, not mine, compared to the owners Bryston 7B's. Similar power but the difference in presentation was very noticeable.

Level 4 skier. Haven't skied in six years. New boots and skies last season, WOW, talk about gear related improvements!

06-21-11: Pani
Since you are moving within the same make and lineup of the amp you will probably not have "inferior" watts.

not necessarily true, AP. the bigger amp *could* have inferior watts; it could have superior watts. It's 50-50 without knowing any more about these 2 Sim Audio amps.
There are several such examples in the industry: the vintage Krell KSA-50 was acknowledged by many users to be a very sweet class-A sounding amp, while the bigger amps in the KSA series such as the 160W or the 200W monos did not have that sweet class-A sound. These bigger Krell amps were really very good but didn't have the 50W amp's sonics. Same could hold true for these Sim Audio amps....

With your speakers it is a big thumbs up to go higher in watts.

based on what???? where's the info or data to support this? have you been reading the manuf website & that's how you know??

What you will most probably hear is a more resolute, disciplined performance because of the grip the amp will have on the drivers. The sound might be bigger as well but it will be more graceful.

based on what?? where is the information or the data to support such a statement. it's pure conjecture on your part....

To Level8skier (from Level0skier!): the question you are asking does not have a definitive answer thru mere written discussion on this forum 'cuz there isn't enough data to supply a good/correct answer.
If you increase the wattage to 250W from 150W, you increase dynamic headroom by 2.2dB. Increasing dynamic headroom is always a good thing for music - you have more peak power that can be delivered into your speakers when there is sudden need from the program material.
That said, another aspect of power amplifiers is its ability to deliver current into the load. That's what sets up the instantaneous voltage in the drivers which creates the amount of pistonic action in them. If your stated wattages are correct, the 150W amp uses a 35VAC transformer whereby the DC rails are +/- 49VDC & the 250W amp uses a 45VAC transformer whereby the DC rails are 63VDC. If the only thing different between the 150W & 250W amp is the power transformer, then, the 250W amp has less load current ability (vs. the 150W amp) 'cuz at higher DC rails, the power transistors can source/sink less current (for a set bias level) according to the SOA graph.
OTOH, if Sim Audio increased the power transformer AND increased the number of output power transistors, you have a higher wattage amp which will have the ability to deliver a higher load current. My understanding is that higher load current is better because the amp is able to maintain is damping factor (DF) better ('cuz as load current increases, the amp output impedance stays relatively unchanged hence DF remains relatively unchanged). In such a case, the 250W amp is a better amp.
You have not told us which way Sim Audio went with the 250W design. Maybe you do not know? Maybe you will never know? Depends on how much Sim Audio wants to share with you....
If you are unable to decide after reading all the available info &/or talking to Sim Audio, it might be better to audition the 250W amp in your house or at your dealer. That would be the best route. In the mean time, all of us can speculate galore for you.... ;-)