To enlarge on the suggestion of testing with a router, inSSIDer etc, I suggest that instead for the convenience of not needing Mains, you load inSSIDer 2 on one laptop or netbook; and Connectify on another laptop, their batteries giving you greater freedom to roam around etc, testing different locations.
I find inSSIDer 2 more convenient than later versions.
If I remember correctly, the free version of Connectify switches OFF after about 30 minutes; but is readily restarted.
I suspect that given that 5 GHz Wi Fi is still not too common, you should concentrate on 2.4 GHz as giving generally better penetration and coverage.
When I tested around my house, garden etc, 5 GHz was generally 10 db worse/lower than 2.4 GHz, the source being an EE Brightbox 2, so a "regular" Wi Fi source, in its normal working location..