In a ute? is 250rms from a single 10 a decent amount of sub? would a 300rms 10 inch be better?
Im able to buy an ampliier that will run at 300rms, and its a monoblock, but will i hurt the amp if i run it at full tilt?
Also, another stupid question, if my front speakers start to distort when they're connected to the headunit and i turn it up pretty loud, how will an amplifier help?
A subs rated input power isn't really an indicator of how well it will play.
How much you spend on the sub itself, how well you design the enclosure, and how well you are able to tune it, will effect how well it plays.
Your front speakers could be distorting for many reasons.
1- The head unit's in built amp. You see the 50 x 4 or there abouts rating it has, well in rms, thats about 12-15 give or take. When any amplifier (in this case the in built head unit amp) reaches it power output, it can no longer deliver a clean signal. This leads to distortion that is then played back though the speakers. So having an external amplifier, allows you to provide closer to the speakers rated input power, without reaching it's limit and going into distortion (clipping)
2- The tuning. Have do you have your speakers tuned and setup? If you are running then in full pass then their power handling will be limited. Try starting off at about 80 hz HPF, and see how they sound. But again, without power behind them, the head unit will still reach it's limit fairly quickly.