Good question and not an easy one to answer!
Have you heard that old adage about people always want a low price, high speed and high quality when it comes to having work done, but that you can only have two, well big wall boots are a bit like this?
The first question is how much free climbing are you doing and how much aiding? On routes with a lot of free then you’re going to have to go for comfy rock boots, and put up with some pain when aiding (the pain makes you get up aid sections quicker), probably having trainers clipped to your harness or in the haul bag for seconding and approach/descents.
On more moderate climbing where there are more aid and jiggery-pokery (french free) then a slightly tighter pair of sticky approach shoes (get thick insoles that can be removed when off the route). This will allow you to free climb a few grades below your limit, climb at your limit by pulling on gear and aid low-intensity pitches without much pain (30/60 min aid pitches). This kind of approach has been used to great effect by people like Colin Haley and others in Patagonia. On some aid routes being able to ‘bust a move’ is super handy, as it allows you to chop tens of minutes off routes, and just being able to step out of your aiders and steady yourself can make moves easier.
The downside with this approach is that if the pitch times (length of time standing in aiders) increases then you’re toes will get very hammered and your insteps with get very sore.
For more intensive aid pitches you need a stiffer boot with plenty of toe room and a solid instep. The type of boot that best fills this is probably you’re bog standard B2 or B3 walking boots. The downside is that they are hard to climb in (ie scary) on some types of terrain, but on hard aid that’s not a problem, and have comfy feet really makes focusing on the pro much easier!
Most big wall boots try and do all of the above, and so are usually a comprise in all camps, and are great for routes without too much intensive aid. The current boots I’m using are Sportiva Ganda Guides, a mid-length boot with sticky rubber, kind of a cross between an approach shoe and a rock boot (more lent towards approach shoe than rock). Found these great for climbing (think Colin Haley uses the shoe version), and OK for aid, but for hard aid routes I’d probably go for a light proper boot like a Trango or walking but with a full shank.
Whatever you get it will get hammered, and the toes will get a beating, so make sure whatever you have has a good toe bumper and prepared to do some DIY before it wears down to the leather.
You made a point about this being for summer climbs, but I did once see the late Charlie Fowler doing the Shield in a pair of plastic boots - but then he was a hardman!