I went for English font pressed metal plates, plain at the front and with a GB flash at the rear (no tax circles or dashes or anything).
Got pulled over (for other reasons, entirely innocent) and actually asked the traffic cop about them, apparently there's 7 aspects of a plate to make it legal and he was perfectly happy with mine. From memory, colour, font, spacing, reflectivity, postcode of maker (but only if plates made after a certain date), position on car were some of them.
I'd be pissed if I did get pulled, given the number of X-f**king-5s I see with black/silver plates, not to mention some of the most creative spacing I've ever seen (AK54 MXS turns into black/silver AKSAM X5 - I'm looking at you here...)
I run a 3-digit Irish plate and to be honest on pressed metal (on my Audi Coupe GT) it looks way cooler than a plastic one.