In computers there is something true regarding HDD/SSD and RAM. They are all expensive on the spur of the moment, sometimes cost prohibitive for some. If you really need speed, I'd suggest getting the SSD. The bottleneck is narrower in an HDD vs RAM. So getting an SSD will widen that bottleneck and speed things up.
However, if you need the speed bumps, but can wait sometime, then I suggest waiting around 8 months. By this time 256 GB SSDs will have dropped in price tremendously and 8 GB DDR3 of RAM will be even more affordable (compared to $1.2k from Apple). Look right now, DDR3 price dropped fast to todays more reasonable prices vs the prices just after the new unibody MacBooks. From that small event I take it 8GB will be affordable to the average end-user.
You wanna talk real bottleneck in speeds? The FSB is going to be your killer, no matter how fast your CPU is, the FSB is going to be the one that actually dictates your machines crunch. Luckily and thank God, Intel is finally getting rid of the FSB.