Get the wider lens for now, at 50mm you have a short telephoto lens very usable for portraits.
When you're getting more into portraits you can get the 5-135 or 50-150 to fill the spot.

I went the other way, bought the DA*50-135 for portraits first and then bought the DA*16-50 for normal photography.

The two lenses at those ranges work very well together, at least for me.

Hmmm i haven't said that

Mowog just read your first comments, you say nothing there about lenses or even talk about the crop factor so how are we supposed to know?
Only with your fifth comment it comes apparent that you're talking about the crop factor.

Do you find it strange that people get confused?

The K5 has the option to switch DFS off

The DA*16-50 is a pro grade lens, most likely you can force extra guarantee, the only problem is that you need to prove it's because Pentax did something wrong.

Or a KX although that one lacks weathersealing, don't know if that's a must.

The Sigma 15-30 & Sigma 28-70 are lenses that compliment each other not replace each other.

The 28-70 is a constant f/2.8 lens and goes pretty wide, good for most portrait work.
The sigma 15-30 on the other is not a constant aperture and the lens is too wide to use for portrait work.

In your case I would look at the 17-70 offerings from Pentax and Sigma.
Another option is to see and wait how the Pentax 18-135 would be.

btw you've the Pentax 28-80 3.5-5.6 and Sigma 18-35/3.5-4.5, aren't those good enough?

If you're looking for high quality than the Pentax 16-50, Tamron 17-50 Sigma 17-50 would be your better bed.
At 50mm you can do portraits easily and they are all constant f/2.8

The UK deliver cost they normally apply is subtracted of the total cost if the item is shipped abroad.
At least that's what happen when I bought the DA*50-135 from them a year or a bit longer ago.

This what Chris said to me.

Hi Stefan,
Although we cannot offer free shipping, we take the value of the UK postage and knock it off the postage costs which saves you £8!

If you wanted to order a lens from us, just order it via the website but you will have to select United Kingdom from the country selection. Then put your full address in the customer notes section. The alternative is we can take paypal - if you want to pay this way let me know what you want and I can send a money request by Paypal. This is probably the easiest method!!

If you can do the math though, I'm sure taking into account the 1.5x crop wouldn't be a problem

Wow that sounds great link