^^^ I see a lot of recommendations of people telling you how to spend your money, but no one is telling you how to find the right solution. The brand and driver are not important, you need to find the right specs before you commit to anything.
You need to look at the SPL @ 1 watt spec. The other thing to look at xmax, but you need to consider how much you need, more importantly "don't" need. With 600 watts as say 88dB @ 1 watt (an average 15" car woofer), you might not be able to push that past 10-15mm xmax depending on what kind of box you use. If you cut xmax, you cna usally increase SPL @ 1 watt by looking at higher output pro-audio like drivers. So you can ditch the 88dB for maybe a 92dB @ 1 watt driver that maybe has 15mm of xmax rather than 30. xmax is usually a tradeoff of sensitivity.
my brother only had about 600 watts to play with in his car and i built him a custom 15" TC9 driver that had about 94dB @ 1 watt and a good 15mm xmax. That thing absolutely pounds.