I figured putting this rule together was a reasonable start:

`@RULE ReallySlow`

1 tape ON

2 tape OFF

3 tape advance

4 ticker right

5 ticker left

@TABLE

n_states:6

neighborhood:Moore

symmetries:none

var a = {0,1,2,3,4}

var b = a

var c = b

var d = c

var e = d

var f = e

var g = f

var h = g

var A = {1,2,3,4}

var B = A

var C = B

var D = C

#tape counts up

1,a,b,c,0,0,0,3,d,3

2,a,b,c,0,0,0,3,d,1

2,a,b,c,0,0,0,0,d,3

3,a,b,c,0,0,0,d,e,2

#ticker ticks up

0,0,0,0,a,1,b,4,0,4

0,0,0,0,a,b,0,4,0,4

4,0,0,0,1,A,b,0,0,0

4,0,0,0,a,0,0,0,0,0

4,0,0,0,0,a,b,0,0,0

#ticker ticks down

0,0,0,0,0,0,A,4,0,5

0,0,0,0,0,0,0,A,4,2

A,5,0,b,0,0,0,C,0,2

A,0,5,b,0,0,0,C,0,2

0,0,0,5,a,B,c,0,0,5

5,0,0,0,a,b,C,0,0,0

5,0,0,0,A,B,0,0,0,4

A,5,0,B,0,0,0,0,0,0

Spaceships in this rule consist of a state-3 cell with a state-4 cell above it and any number (including 0) of state-2 cells to the right of it.

A 2x1 spaceship is p4, and periods for longer ships increase roughly exponentially with length.

More specifically, if a 2-by-X spaceship is pN, then the next ship's period is 2N - (2X+1).

The first few periods:

`x = 21, y = 47, rule = ReallySlow`

6.B.B$6.B.B4.D$6.3B4.C$8.B$8.B2$6.3B$8.B4.D$8.B4.CB$8.B$8.B2$6.B.B$6.

B.B4.D$6.B.B4.C2B$6.B.B$6.B.B2$4.B.3B$4.B3.B4.D$4.B3.B4.C3B$4.B3.B$4.

B3.B2$2.3B.3B$4.B3.B4.D$2.3B3.B4.C4B$2.B5.B$2.3B3.B2$2.B.B.3B$2.B.B.B

6.D$2.3B.3B4.C5B$4.B3.B$4.B.3B2$2.3B.3B$4.B.B.B4.D$4.B.3B4.C6B$4.B3.B

$4.B.3B2$B.B.B.3B$B.B.B.B6.D$B.3B.3B4.C7B$B3.B3.B$B3.B.3B!

The 2x21 ship is our "passenger airline", with a speed of c/1048619 or 286 meters/sec:

`x = 21, y = 2, rule = ReallySlow`

D$C20B!

2x28 gets you down to just over 1 meter/sec, or a good walking speed:

`x = 66, y = 5, rule = ReallySlow`

3B.3B.3B.B.B.3B.3B.3B.B.3B$2.B.B3.B.B.B.B3.B.B3.B3.B.B6.D$3B.3B.3B.3B

.3B.3B.3B.B.3B4.C28B$B3.B.B.B.B3.B3.B3.B3.B.B3.B$3B.3B.3B3.B.3B.3B.3B

.B.3B!

2x36 (p34,359,738,441) is just a bit slower than a snail, and 2x62 moves about as fast as Mount Everest grows naturally.

Any other methods of compactly creating arbitrarily slow speeds that people can come up with?