What kind of pendant do you like, solitaire (single stone), center diamond with a halo, or other style? What diamond shape are you looking for, round, princess, pear, or other?
I guess for everyday wear, a simple solitaire diamond pendant is best. Unfortunately, I do not have one. I have halo pendant and Circle of Life pendant, but never got around to getting an everyday, solitaire pendant. Both of my diamond pendants are too dressy for everyday wear.
Since I have been thinking about getting a solitaire diamond pendant myself someday, I have done some research and thinking. First, let us talk about the setting. I would like the diamond be free to slide on the chain. Due to the relatively light weight of the solitaire diamond, the diamond will have a tendency to run up my neck to the side or even the back. Having to constantly adjust the diamond position will drive me crazy. Therefore, I would avoid any light pendant that is attached to the chain.
Second, let us discuss the diamond and budget. I would put most of the money on the diamond, so I can get, for my budget, the largest possible, best cut diamond that is I color minimum (not too much tint) and eye-clean VS2 to Si1 clarity. The pendant setting costs around $500-$600. GBP 4500 is about $6300 budget. That leaves about $5700 for the diamond. Whiteflash has an ACA (top cut) diamond that i like best and that fits your budget. The diamond is 0.933 ct, graded by AGS, H color, eye clean SI 1 clarity for $5,717. The dimensions are 6.25x6.27x3.88mm.
For diamond advice and guidance, I suggest you go to Pricescope (diamond forum) for help.