SRT is only good if you need the extra space. It will improve your most used applications by placing a copy of them of the SSD, but will lack the full out speed boost of an SSD alone.
Also note that it is a good idea to leave some free space on most SSDs so the controller can do wear leveling.
If you are just going to run your software and not fill the system with games and the SSD has the needed space, go that route.
I would agree with the poster above, 128gig SSD's tend to out perform 64 gig ones by a fair margin, but if it is not in the budget, its not.