does anyone know whats the max speed i can convert up to on a 89 cannondale 3.0 sr600?

Measure between the rear drop outs. If it is 130 mm, then you can go up to 10 speed (shimano/SRAM) or 11 speed (campagnolo).

Technically, 7 speeds, because 8 speed and up is 130mm spacing while your frame is 126. That frame is pretty stiff, making it tough to squeeze a wider hub in there, but it can be done.

ok how hard would it be and what would be needed to get a 10 speed hub in there

You need 2 strong hands to hold the dropouts an extra 4mm apart when you put the wheel in there. The annoying thing is you have to do it every time. It's not recommended that you try to cold set an aluminum frame. I've also even heard people claim that forcing a 130mm hub in it all the time leads to cracks, but I've never seen that verified, and I saw people do this to your exact frame all the time in the 90's when STI first came out.

I personally wouldn't bother, but you may have your reasons.

ok so best option if i want brifters is to look for some old rsx's?

I could be wrong, but I thought RSX still used the freehub spacing on a 130mm hub.

I wonder if Sheldon Brown has a take on this. I'm sure you're not the only one who's played with this idea.

oh i saw 7 speed rsx's on ebay so i assumed theyd fit since they are from same timeline

I've converted my 1986 Cannondale to Campy 10 speed. No big deal. Yes, it takes a bit of oomph to spread the dropouts when inserting the rear wheel, but I only do it a few times a year for a flat or new tire.

Well, I was an elitist snob in the 90's and only ran Ultegra or Dura Ace. Maybe somebody else can chime in on RSX specs.

idk if i honestly wanna deal with that,is there any differences imma miss out on being only 7 speed?

my friend just updated his cassette to a 11-28 7-speed... we had to take the 13 and 14 off his 13-23 cassette so he could have something less that crap for shifting granularity... as in... 11-13-15-18-21-24-28... that cassette sucks... but not as much as having NO climbing... so we took it. and did 13-14-15-18-21-24-28... better than total suck. Going to an 8 or 9 to get some better shifting in the top end (smaller gears) is worth it if you ever plan on climbing with a 53/42 like so many older bikes have. Sometimes I find myself shifting twice to adjust on the big cogs, but I always like the tight shifts in the small cogs.

You have less gears to choose from, and you miss the convenience of integrated shifters.
Worth the trouble and expense for me, maybe not for you.