What tonearm will better mine?


I have been running a 12" Jelco SA750L with an upgraded Decca Super Gold on a Garrard 401 for a few years. I'm happy with the sound and happy with my pre, power and speakers. (Croft 25R, EICO HF35s, -good tubes, Quad 57).
I keep hearing that my tonearm is a weak link even though it sounds pretty awesome to me. What would it take to replace the Jelco and make a significant improvement? What should I expect to hear better? Would I have to drill the massive plinth? Thanks.
128x128noromance
Op, my advise is simple. If you like your sound, don't worry about what the others say and be happy.  Our hobby is endless. :)  Always pushing for a better sound and to what end.  I use a Jelco 750D tonearm on a restored Thorens 160 Super.  It's a great arm, I see no point in spending 2-3x the money to get little improvement.  Trust your ears! Good luck! 
bdp24, Wow ! I´m glad you ordered that superb T3Pro linear TA. 
Mine is also made with an uninterrupted run of silver wire to RCA plugs.
I´m also planning to try silver Eichmann plugs. Are yours the same (or equivalent ) as these on eBay:
http://www.ebay.co.uk/itm/KLE-Innovations-Silver-Harmony-RCA-Plugs-Set-of-4-/131438981244?hash=item1...

Harold, KLE makes it kind of confusing, with their name designation. The RCA jack line ascends in this order: Classic Harmony, Copper Harmony, Silver Harmony, Pure Harmony, and at the top Absolute Harmony, which is what I sent Vic. PM me for more details---Eric.

Last night, I added the Ammonite collar and the Expressimo Audio brass stub and counterweight to a black 12" Jelco 750L (401 on slate plinth). Both are extremely well made. I did the mods one at a time and the most impact was obtained from the brass stub/CW. Scott Hamilton - Is a Good Wind Who Is Blowing Us No III -increased speed and air on the edge of brush drums. More blackness etc. Not huge but enough to be worth it and it looks awesome. The collar didn't make as big a difference as far as I could ascertain but I may have messed up the test by running on cold tube amps. All in all worthwhile and easy upgrades.