I would not suggest a solid state drive (SSD) for a ps3. There were even negligible differences in 5400RPM vs 7200RPM; also, i believe, at least for the phat models, that ps3 only runs on SATA/150 so it will just downrank any SATA/300 you put in. I personally run a Western Digital 500GB (WD5000BEVT) and my system seems to have sped up from the increased room for the game data and what not; I have a MGS4 PS3 phat too (model# is CHECHA, i think.)
The more you play the better it shall get loading time wise. Tsukuba is my most played track so it loads quite quickly whenever I go to it. I don't know whether or not it makes a difference from the initial install or not, but in the settings on the last menu section there is a "diagnostics" menu and in there there is an option to pre-install data, but i do suspect that it is the same thing as the initial install. Haven't tried it yet, too busy playing when i do have the freetime.