the performance gain on a hybrid drive is pretty small for what your paying for it. its better to have a ssd/hdd combo for now. Hybrid drives are still pretty new and not enough companies have put effort into it yet. expect to see more in the following year though.
Which is faster a hybrid 500GB/750gb HD with 4gb/8gb SSD or a 1TB hard drive with Raid 0 especially with regards to a gaming laptop.
Neither is particularly fast for gaming.
4/8gb is not really large enough on a hybrid hard drive to hold what you will use for a day. The extra speed comes only for what is in the ssd cache at the time.
Raid-0, assuming the laptop can have two drives is slightly faster in sequential access.
If you want any sort of significant improvement in drive performance, install a ssd. a 120gb ssd will hold the os and a handful of games.
For gaming, get the best graphics you can afford first.
Do you think a $200 upgrade for a 256 gb SSD is worth it?
It depends on how much storage you will need, and what your options are if you run out.
SSD prices are declining, and will probably continue to drop. In a few years, you can probably replace a 120gb ssd with a 240gb ssd and not pay any more in total.
If you will need more storage space, one possibility is to use an external USB attached device.
That is not a bad idea, anyway. You could use it to backup the files you cherish to an external device.
If you laptop will have the ability to hold two drives, then adding storage later is easy.
If the money is not a great show stopper, 256gb might be a good idea if you think you will fill it up.
What really takes up space is video files.
One option you might consider is buying a laptop which includes the smallest, slowest, cheapest hard drive, and replacing it yourself with a SSD. It is not hard to do. Laptop vendors tend to charge a premium for including a ssd.