There are limits here on what is practical and workable.
In this case you have a PowerPC based system so your OS can't be upgraded past a set point which gets into how the OS works with SSD drives. In your case TRIM services are not available so your new SSD will not wear well.
Your systems HD interface is quite old SATA I (1.5 Gb/s) so anything you get will need to function at this I/O speed. So a lot of the improvement you are expecting won't be there as most SSD's run at SATA III (6.0 Gb/s) note the difference in data rate.
To be blunt here I don't think spending your money on a SSD is worth it.
I think you will gain more upping the RAM as well as setting up RAID across a second PCI interface if you plan to hold on to this system. Yes, a SSHD hi-bred drive can give you better performance if you don't want to get into RAID 5. Here's a good writeup on RAID and here's one on your Mac OS-X options Using OS-X Disk Utility. Some options may not be possible with your OS.
Otherwise I would bank my money to buy a newer Intel based system (if you want a screamer the new Mac Pro's will blow you away). A iMac or Mac mini will also go far.
Sorry for the let down.