Thanks for all the great suggestions! During the past month, i have continued my research into keyboards, and I have taken the plunge on quite a few. This has cost me plenty, but if I can bear to part with the least favorite of them, I might be selling some of the boards. Here is the roundup, with some brief impressions:
1. Found a NIB IBM SSK! Being accustomed to a full-size Model M, the SSK has the familiar buckling spring switches and dye-sub PBT keycaps in a two-tone ivory and beige color scheme that I prefer. My speed and accuracy are better on this board than any other I have tried. Both the full-size Model M and the SSK give me a feeling of confidence when I type, and the build quality of these boards is second to none. The SSK has become my new daily driver, but having scaled down from full-size to TKL, my appetite has been whetted for smaller TKLs and sub-TKLs, all the way down to 60% boards.
2. Filco MJ2 TKL Ninja with Cherry blue switches. Exchanged the keycaps with the Classic Beige with Blue doubleshot set from Originative. I like the build quality, appearance, and smaller size of this TKL, but I don't like the feel of ABS keycaps.
3. Ducky Chinese Edition TKL with red LEDs and Cherry brown switches. Build quality of this board is relatively poor -- the case is not straight and so the board wobbles. The extensible feet are not rubberized, and so the board slips on the desk. I like the red LEDs in the low light of my office, but the appearance of the board is not that great when the LEDs are off.
4. CM RF Stealth TKL with Cherry green switches. This board is on backorder. The board gets generally good reviews, and I am eager to try out the green switches.
5. Leopold FC660C (Topre 45 g switches). This board is on backorder. It gets very positive reviews, and I am eager to try out the Topre switches.
6. Leopold FC660M with Cherry blue switches. I am typing on this at the moment. This board has an elegant layout. It is essentially a 60%, but with added arrow keys as well as insert and delete keys. The main typing area is mostly standard, but the right-shift is the same size as the left-shift, and it has a single Win key on the left. The spacebar also has non-standard spacing of the stems. The Fn layer is sparse and highly intutive. Build quality is excellent with a very solid feel. The keycaps are PBT, but too dark for good visibility, so I replaced them with a mix of gray and white dye-sub PBT Cyrillics from Originative. I also did an O-ring mod with 40A-L (red) rings; now the board is quiet enough for use during conference calls. Although there are some things I would change about this keyboard, it is currently my second favorite next to the IBM Model M.
Although I have already invested a small fortune in keyboards, and I have found two that I really like thus far, I remain intrigued by the challenge of reproducing full-size function in a 60% layout. At the moment, I am looking at the Filco Minila, KBT Poker II, KBC Pure Pro, and Tex Beetle. At first, the Minila looked too bizarre, but after studying the layout, I have come to appreciate its logic. I have heard that the Pure Pro might suffer from some quality issues. The Poker II would be the easiest to customize owing to its standard layout, and the Beetle appears to have excellent build quality and a handsome brushed aluminum top. I cannot seem to make a choice among these 60% contenders, and I would welcome further thoughts and suggestions.