The i5 will offer better Performance in pretty much everything except integrated graphics. The only reason to for the a8 if for better integrated graphics but even then a discrete card will still blow it out of the water. The i5 is usually better for everything else.
I had an A8-4500M with 7640g + HD7670M while my friend had an i5-3320M with GT 630M. On programs that rely more cpu power his was a clearly better though in multithreaded workloads the A8 showed that it can at least catch up to the i5. In terms of gaming, the 630M gave better performance mostly because my A8 had a some micro stutter problems but otherwise the performance was very similar, in your case if you are only looking at the cpu without any discrete gpu than the A8 would give you better graphical performance (as you already seem to know, though about more heat generating, I didnt experience that but I also did update the thermal paste of my laptop with an aftermarket compound, but yes, my friends i5 laptop seemed to stay cooler more often then not)
Later I upgraded the cpu from A8 to an A10-4600M on same laptop, the results improved but the i5 for the most part was better still though, now the cpu not only caught up to the i5 in multi threaded workloads but could just as easy beat it. Also with that upgrade my gpu section was now a 7660g + HD 7670M, the performance was better on my laptop on most games but micro stutter would still rear its ugly head again (not sure if the stuttering has been resolved now)
Simply put if you are buying an laptop with no discrete gpu then I would take an A8 or A10 over the i5, not just for the overall performance but also the lower prices they come with. Now with a discrete gpu on laptop most likely I would take the i5, though if the gpu is a 630M I would rather take the AMD machine (mainly because I didnt see a big difference at all between my friends machine and mine and at that time he payed over $100 more than me).
If you are looking for just cpu performance the i5 are much better overall (whether the haswell or ivy bridge models), if you include the i7s then its just becomes unfair