Looking through the forums I see many mentions of the heat factor in March. Is it totally stupid to consider a trip to the Golden Triangle in May?

If you are a backpacker it would be inadvisable. If you go the five-star route, it is doable - deluxe hotels, air-conditioned cars etc. If you are a first-time visitor to India, it is highly recommended that you wait the weather is optimal - it will play a big role in your perception of the country.

In May, head for the mountains. Sikkim, Uttar Pradesh, the hills of Karnataka & Maharashtra, & maybe Kashmir. These places are where we're heading. Obviously the best time to see Rajasthan is Nov-Feb but there are many other parts of India which should be beautiful in May.

Forget Uttar Pradesh in May. I meant Uttaranchal! Around Landour-head for the hills!

May will be hot, hot. Great time for malaria, dehydration, etc. However, if you are a seasoned traveller and plan to take A/C buses, trains, planes then it's fine as I know people who have gone in August and did not get sick.

I went for the whole month of April and it was boiling but just remember to drink LOTS of water and I squeezed fresh lemon in mine to help with bloating from drinking so much. Don't eat any food from street vendors, always make sure everything is piping hot when you eat it. Tempting as freshly squeezed juices and smells of food being cooked on the street, DON'T DO IT!

February is the best month to go.

Not a good idea IMHO. Temps can hit 110-115 F. You would survive it but not enjoy it very well. I would say don't go then.