If I was looking for a 2 man tent, I think I'd almost certainly go for the Nallo. Reviews over the years consistently put it at the top of the class. It's stable, reliable, roomy, beautifully made and no heavier than it needs to be. It's a truly lovely tent.
I was not trying to encourage you to go for a heavy 6kg tent. Just to tell you that weight is not always everything especially when split between people so don't rule heavier tents out immediately without looking carefully at your needs.
You should be able to find something between 2 & 6kg at a price that suits. The tents you have mentioned will probably both be fine. I tend to be all or nothing - If I want a mountain tent I will get the best/strongest I can afford that suits my need.
Like most things, with tents you generally get what you pay for. Wether it is worth the extra cash to get brand x over y is down to the individual.
Maybe in the future Ill be able to afford more than one tent - at the moment Im after a tent that will do everything - what with being at college, because I aint going to be able to borrow the one Im using for much longer and dont fancy resorting to my dads (25+ years) Force 10...
Backpackingf (like life) can be one big compromise:-(
Your dad's force tent will probably be very good if it has been looked after. Ridge tents are still used on many serious expeditions due to their strength, simplicity and easy maintenance.
The problem is if it is cotton, it will be heavy and may have succumed to moths/ mould etc if it has been abused and or poorly stored. Also the triangular interior does not leave much headroom.
If you are on a budget but don't want too heavy a tent I would still recommend the Vango Spirit 200.
You can often get them for under £200. They are similar in design to Hilleberg, and although not such high quality, Vango are still reliable. I've never used one myself but 2.7kg for a two person tent with a massive porch for £200 sounds like a good compromise to me.
Alternatively a lightwave t2 trek with the extended porch would also be a good value buy.
If you are at college I see no need to break the bank with a hilleberg. Use the money you save to go on nice trips!
Late curve ball - You can get a macpac Minaret for £203 from Snow and Rock.
That's the Ed's favourite tent (there is a review somewhere on OM magic). It'll be better than a Vango and and comparable to the Nallo in design and quality.
It's a tad heavier than a Nallo but its arguably stronger...
You may struggle this time of the year to see all the tents, especially the more exotic/ specialist ones but it is a good time too buy so you may get a cheaper price.
To make the process easier and save some time and travel look at for eg, any of the vango tents in the range you are looking for to see if you like the quality, look at some other similar priced brands and then order from the brand you like.
The same can be said for looking at style-geodesics/ ridge, wedge, hoop tents etc. Decide what you like by looking at a number from various manufacturers. You may decide you like a geodesic tent by looking at say, the north face ve25 but opt for a vango instead as you prefer the brand/quality etc.
Most tents brochures indicate weight, dimensions and have reasonable pics detailing the tent features etc so this will probably not be a problem if you can't see your particular tent.
Lastly use the forum as you have to re-enforce what you probably already have worked out.