Generally a small block (by virtue of its superior head design, i.e, Valve angle, position in the bore, port area for nominal displacement) will make more horsepower per cube than a B/RB. By that I simply mean starting in stock form it's easier to make a 400 horse 340 than it is to make a 515 horse 440 (same hp per cube).

But most economical is to start with more cubes without stroking so it's easier to make say a 515 horse 440 than it is to build a 475 horse stroker 408, (again same hp/cube) so starting with a bigger motor to start is most economical. $1 in the heads is worth $3 in the shortblock, it's a good rule of thumb, and so if that shortblock is already bigger you're that much ahead.

My fwiw, You can build a bullet proof stock stroke steel crank 440 that will make 600 hp easier than you can build a 550 horse 408 stroker out of a 360, $1 in the heads is worth 3 in the shortblock.

Best bang for the buck for ~600 horse is a zero deck ~11:1 steel crank 440 with well ported indy SR heads that flow about 335-340 on the intake, a good solid cam in the 255/260 @.050 range and .560 to .580-ish lift cut on 108 in at 105, 1 7/8 or 2" headers, full 3" exhaust, a good ported single plane (or ported indy dual plane) intake, and at least an 850 double pumper. ( a 950 will be better up top) I'd say this would compare in HP/ET to about a 565 horse 408 in the same car with very well ported E heads. the difference is you can build the 440 for less.

Strokers are great but there's absolutely nothing wrong with a solidly built well thought out 'old school' 440

600 horses could put a 3400 pound (with driver) car in the mid 10's but the stall and chassis need to be dialed dead-on and you can't do it with 3.55 gears. (4.10's) The basic motor I've lined out (one I've built several times) will make about 630 or 1.4 hp/cube, and peak power right around 6100-6200 with very strong torque.

I don't think you could build a 408 with comparable power per cube (and you'd actually need more per cube since the motor is only about 60 pound lighter) for the same $$$. A good builder could get close with (for example) a set of well ported econo w2's and a cast crank to save $$$.