Should I buy a bigger amp or get an amp that matches my subs?

Never overpower speakers. They will clip, distort and burn out. Get an amp that matches the speakers. An amp with more power than speakers can handle may be carefully used, but there will come a day when you leave passengers hands unfettered and someone will say, "OOOOOH, That's My Sooooong!), and pop the volume to max. Hopefully the amp goes into protection before there's damage. If you happen to be in the store during the event, all you'll get is a burned smell and an apology prefixed with, "Yo stereo just up and quit, man."... Lay a beating on them, unless it's your sweetheart, then just a hard slap will have to do. The 300 RMS watt amp would do a very respectable job on the 400 RMS watt speaker you have. The 800 RMS watt amp would be very much like pulling the pin on a hand grenade. Anybody telling you to go for the 750.1 or the 1000.1 just wants you to destroy your speaker for their amusement.