There's a lot been said here that's correct but quite a lot that isn't. Firstly, you're focusing far too much here on colour depth. You're correct that 8 bits/component is desirable for smoother gradients and reduced/no use of FRC, BUT that's not the most noticeable benefit of IPS. The crucial difference is colour shift. With a TN panel, colour will never be displayed the same from top to bottom of the screen.
As your eyes are level with the bottom of the display you'll see colour at the bottom becomes far stronger and more vibrant. But look at fine details in on dark/black backgrounds and they'll disappear as your eye level is closer. The top of the screen from this angle will look faded and washed out, but those fine details are highly visible. Move your eyes up towards the top and you'll see those details fade into black as the top colour becomes stronger/deeper, while the bottom of the screen will become too dark.
Obviously in practice your eye level will be central (or 1/4 down, 2/3 down etc). That means that colour above eye level will always be weaker and colour below will be darker and suffer a loss of detail in dark areas. You can test it yourself - get a photo or game wallpaper on your desktop (something with a variety of colours) and move your head up and down - see how the colours and detail shift. Be warned - you will look silly doing this.
With IPS, do the same as you will see zero colour shift. Colour will be flawless, strong, vibrant across the entire screen and all fine detail will be flawlessly preserved. Like I say, 8 bits/component colour depth is absolutely desirable, but it's not the main point.
The stuff about IPS being too light is not entirely correct either. Your IPS monitor will be too bright initially (at 100%) but that's the same with TN film panels and PLS panels, PVA, AMVA... it's universal. There's nothing inherently too bright about IPS :-)
If exceptional deep blacks are important to you, you won't get them from IPS, but you won't from TN either. Or MVA/AMVA. For that you'd need a PVA panel. I'm not recommending that (though I use one myself and it's awesome) because they're rarely sold and they make other compromises. But it's important to highlight that
every TFT panel is a compromise. There is no perfect panel type that leads in every area.
So the fastest TN panels will have superior pixel response, but that certainly doesn't mean they all do. The fastest IPS panels are faster than most TN panels - just the fastest TN are even faster still. And when I talk about speed, I'm not talking about the manufacturer-quoted specs - they're absolute crap.
Please disregard those are use a professional monitor review site like
www.tftcentral.co.uk to compare high-speed photography results.
For a combination of both quality and speed, your best all-rounder is an IPS or PLS panel with excellent RTC overdrive (which applies increased voltage to high-contrast pixel switching in order to improve response). Almost all monitor manufacturers have some kind of RTC implementation, but some are far more effective than others. Among reasonably-priced displays, ASUS's Trace Free is the absolute best of these. I'd recommend these models:
ML229H
ML239H
PA238Q
PB238Q
VG23AH
MX239H
PA248Q
MX279H
PB278Q
Trace Free gives more granular control over the overdrive impulse, and that's really important for effectively eliminating trails. Problem is, too much voltage applied means you get 'overshoot' - an inverting of the trails. You're simply swapping one type of trail for another. Many manufacturer's RTC implementations are guilty of this. Options are limited to on/off or off/medium/high and none are exactly right (think of it as like a focal point on a camera). Trace Free gives options of 0, 20, 40, 60, 80 and 100. 40 gives best results on most ASUS models. Alternatively, Iiyama's implementation also gives a lot of control (-2, -1, 0, +1 and +2 settings). For Iiyama:
ProLite X2377HDS
ProLite XB2380HS
ProLite X2485WS
ProLite XB2485WSU
Oh and 720p is 1280x720 - not 1440x720 (which would be crazy super widescreen :-))
Let me know if you have any other questions.