steve,
I'm sorry to say that I don't have figures such as you request. What I do have is experience with each of the types you describe. The cross-flow head with enough carburetter is no doubt the highest performance, but it's expensive and a bit difficult with which to live, since the distributor is under the carburetters. I know others will disagree, but you did say you wanted an "easy driver".
The standard head can be reworked by someone who knows what they are doing and whom is equipped with the tools to do it and a flow bench. This too, done correctly, will be a tad expensive, and unless you follow it up with a header and improved induction (carburetters) you won't reap the full benefit.
Bang for the buck-wise, I'd reccomend the non-cross-flow alloy unit. Some criticize it as having too large intake ports. This has not seemed a problem for us, and you'd think it would be an even bigger problem here at five thousand feet above sea level. The other things we like are that it is lighter and that it runs much cooler, which will allow you to use a higher compression ratio if you desire it.
Here's our prescription for an power upgrade without laying out huge bucks.
1.non cross flow alloy cyl head
2.mild steel header, sent out for ceramic coating
3.stage one (just above stock) camshaft from one of several makers, with the best lifters
4.vernier adjustable cam sprocket so that you can take advantage of this cam with correct timing. I know this isn't cheap, but it's worth it in spades. This also needs the duplex timing chain and crankshaft sprocket of course.
5.rebuilt, recurved distributor with electronic ignition (we like the Crane unit)
Don't forget to have the connecting rods reconditioned and their big ends resized. Have every rotating or reciprocating major part balanced. Use a new coolant pump, and make sure the oil pump is within tolerances. If there is any doubt, replace it. Also replace the oil pressure relief valve slug and spring. On this engine I wouldn't bother lightening the flywheel unless you are on a quest for every little bit of performance available. Unless it's been done recently, rebuild the carburetters. We actually prefer the HS-4 units over the later ones, but either will do. Don't go to the HS-6 carburetters unless you are willing to sacrifice a bit of low end performance to gain high end horsepower. Of course, there's more you can do, but these mods and procedures are proven by themselves to yeild nice additional performance.
Customers for whom we have applied this "program" to their MGA or MGB engines have been universally pleased. When put on a chassis dynomometer, they have shown a really impressively improved and flat torque line. One MGA customer whose engine we did six tears ago has run about 40,000 miles with zero problems and good power in the mountains out here.
Of course, a good machinist and careful, proper assembly are essential, as is correct breaking in procedure. Anyhow, that's what we do, and it certainly has been working for us. Enjoy the process, however you decide to go.
Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon