A skyloop around the eaves would be noisy and an EMC disaster Andy, especially as you mentioned you wanted to use 400 watts. One thng make sure you have a good earth/ground as near to your station as you can get. You’ll find that 400 watts of power is not necessary for SOTA - you’ll need to hear the activator first and 100 watts is plenty 90% of the time, or wait until the callers are tailing off then less power than that is enough.
Putting a skyloop in the clear would possibly need 4 supports and could be deemed an eyesore by some sado’s or even the XYL. Most neighbours in England don’t like antennas, especially the retired ones with nothing to do but look out of the window. I have 16 neighbours who live with a 400m radius of who banded together a few years ago after I moved in, in an attempt to prevent me putting up aerials. It meant I needed to submit a planning application for a 12m monopole mast and eventually a succesful appeal found in my favour. I’ve challenged neighbours several times over the years, as I have built stations in 8 different homes. I think its worthwhile in the long run if you are serious about the hobby to fight for your rights to erect efficient aerials. It can be stressful taking them on but once they are up and working they tend to leave you alone, providing any EMC issues are dealt with and they are cooperative as well in that.
The only real way to recommend specific aerials to anyone is to know their constraints, see where the house sits on the real estate available, where any supports such as trees or large shrubs are, what access you have to the roof and gable end etc for your mounting brackets. With that information you can then erect what ever you want to fit your interests. If SOTA at this point in the sunspot cycle is your main interest as a Chaser and you don’t benefit from the 20 dB gain you get from using CW then 20m and 40m are your main HF bands for SOTA. So if stealth is important and that is what would please the XYL, a cheap solution as a starting point would be to erect two dipoles fed seperatly for 20m and 40m as high and in the clear and apart from one another as you can get them. A Hexbeam (and probably a Cobweb) with rotator would probably be deemed obtrusive.
See how simple dipoles work for you then either as inverted vees or horizontals. If only one feedpoint is possible I would look at an off centre fed dipole with an ATU as a possiblility. That is what I have found to be a good compromise 80m down to 30m including 60m. It works pretty well on higherbands also but a Hexbeam is much better as it can be turned.
You wouldn’t need the ATU on every band used with an OCFD and if you can get an 80m sized one up then you can get them to match without a tuner very nicely on 40 metres. A full length scaffold pole on your gable end if the layout of the garden is right to support wire antennas of different types could be your (fairly) unobtrusive answer. If you are passing my way (You know where I live) let me know - you are very welcome to call in and you can see what I have done here using trees, shrubs, the house and fences to support various aerials.
PS Yes, a G5RV will work but I think the design has had its day. An OCF Dipole seems to me to outperform the 5RV on most bands and will at least match its performance on 20m I would say.