Cat6 should be good for 10G if installed correctly upto 37m, with variable potential over that to 50odd meters.
Sorry should have checked your current switch spec before commenting on that. As for aggregation, it would make sense between the switch and server/s but 10G to each work station is surely sufficient.
Edit: Further, 10Gbase-T is in my view not a nice connection, its power hungry and has a serialisation delay which makes it not suitable for some applications, but probably not a biggie for yours. I would still do DAC between servers and switch.
No worries.. I plan on SFP+ between the two 1950 switches and the 1950's and the server... The 10GbE will be used for the run from the 1950's to the 1850's and also the two workstations.
Do you think that will be ok, or should I be looking to try and have SFP+ to feed the 1850 switches as well?