I think that the 501 is the way to go for the short term(or even long term). The 501 has a "magic" to it that the 901 doesn't possess, and while the 901 has more detail, the 501 excells in just making great sounding music at a lower price. I've know a couple of people who moved from the 501 to the 901, and yearned for the magic that was in the 501, and was missing in the 901, even though the 901 was noticeably more detailed. I find the 501 to be very Koetsu-like, and I like that. The 501 is no slouch in any department, but it is not the "pinnacle" either. It strikes a very good balance of detail, magic, musicality, and price. I think that unless you have a "super-arm" the 501 is as good as anyone will ever need. Many people have previously considered this cartridge to be very near the top of the last few years crop of cartridges, and that isn't bad, considering its price. If high-value is a consideration, the 501 has to be among the top choices, if not the very top choice. The DL103R at $239 is probably my choice as the very best cartridge for the money, as it approaches the 501 in performance for about 1/3 the cost. Dollar for dollar, you can get more with the DL103R than any other cartidge that I know of. It will flat embarrass alot of much more expensive cartridges. And at $239, you can afford to play your records alot, without even considering stylus wear. It has alot going for it, but it needs a very good arm, with high effective mass, or a HiFi mod.
You know, regarding the OL Silver, I wasn't overly impressed with the appearance either, and it looked very plain. But with a DL103R on it, and a HiFi mod, we were looking at a very good performing package that cost less than most decent arms alone. When I got mine, the OL Silver was only $740, and the DL103R was only $210. The HiFi mod was just pennies. For under $1k, this setup was pulling very close to some very expensive stuff. That meant alot to me, because I can't afford $3k tonearms, and $2k cartridges. Believe me, when I set that stylus down in the record and started to listen, I forgot all about how it looked, or how little it cost(except that I kept smiling about how great it was for so little money). No, it is not the ultimate, but on the "diminishing returns" scale, it is totally out of proportion. It plays very very close to the "big league", for entry level dollars. And with the Shelter 501 in it, it is actually in the "big league" although not at the very top. If performance for the money is important to you, this needs to be considered as a possibility.
And, as Dougdeacon so accurately posted a while back, the HiFi-modded OL Silver could quite possibly be the best tonearm in the world for "leading-edge dynamics". If you look at any "big league" tonearm, they only top the list in one category, or maybe two, at most. There is a "leader" for midrange liquidity, and a leader for bass response, and a leader for etched detail, etc, etc. Any tonearm that leads the pack in any one category, must be considered in the "big leagues" of tonearms. You won't find any other "category leaders" at the price of an OL Silver with a HiFi mod.
For the money spent on a HiFi modded OL Silver, and a DL103R or Shelter 501, you will be painfully close to the top of the heap, for a whole lot less money, and it would be a great sounding package for anyone beginning in this hobby, as well as any very experienced person. Heck, I'm considered pretty experienced in analog, and I run a HiFi modded OL Silver and a Shelter 501 on my Teres 245. And I'll put it up against anything, anytime. Maybe it won't win all the time, but it will be real close at way less money. And it makes me happy with the sound.