power required for 3/400Hz and up

ok, so im looking to build a 'fullrange' horn tower capable of really loud but i don't have unlimited cash. put simply i am wondering how much power a mid range needs/should be able to handle.

selected drivers so far (per tower):
1 fostex 'low end' horn tweeter, does 98 db @ 1w/m will play >5kHz
2 10" kappa perfects optimized in a ported box to play 30 to 3/400Hz
mid???? for the remaining frequencies.

and theirs 3 12's under the couch for down to 20Hz

i was looking at the fostex 3" 'fullrange', it did 88 db @ 1w/m and math suggests an appropriate front horn would boost that and average of 10 db, so it will be on par with the tweeter. however i looked at the power handeling and it was 10w!! and according to my simple calculations that would yield an ultimate db of 107db assuming a doubling of power increases db by +3, between 1 and 10 there are 3 full doubles plus the 10db horn gain. this doesn't seem that loud :S the tweeter can handle 50w.

so do i pick a different driver or use multiple midhorns? i noticed the larger fostex full range drivers were more efficient and had higher power handeling, so i was considering up to a 5", otherwise i was looking at other companies.

basically im presuming high efficiency and high power handeling equals mega loudness. and i want a flat response.