I'd draw the line at 2kg to be honest (4lb in old money). Anything more than that and you'll really feel the weight penalty once you've added on all your other camping gear. I'd certainly rule the Vango Halo out.
Some would differ with your view slioch - particularly using a one man tent - many find them cramped for one - especially if you want all of your junk in the tent with you.
Personally I think you can go up to 2.5 or 3kg.
My robens Lodge 2 (2 man used for one person) is at the upper limit of that and I don't find it a serious issue at all.
I did go a bit mad recently and buy, at a good price, a Vango Halo 300XD. That's a three man tent for just me. The XD means its super tough with hardier components right down the zips. It's aimed at marauding groups of scouts and guides I think. That I may come to regret -that is pushing 5kg!!!
I think I'll keep it for trips where I am staying put a while - and where I can bag a cheap campsite fee for turning up on a bike - then unpacking the palatial monster
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It does actually pack up pretty well - but yes it is heavy.
I don't think you necessarily need to spend a shedload of money on a tent (particularly if buying in the sale season) as a with a lot of the more expensive tents you are paying for reduced weight - and in some cases possibly too reduced - not as tough.