I remember George (prime95) pointed out somewhen that there is a big speed diference between 100 MB allocated and 200MB allocated, but not such a big one between 200 and 400 MB (or 400 and 800). In other words: more mem is better, but the speed increase is not even linear.
So I guess you can save the money and buy something else, an for example, as IMHO it's quite OK is you give say 350MB to prime95.
If you want absolutely increase your throughput with that money, you may buy another old machine with few mem and let it run only stage1, transferring the save files to your more recent machine. But...
Other opinions?
Yours H.