rk (runge-kutta) of dynamics package really slow?

I tried to numerically solve a system of ODE's with maxima's rk function but 
it takes ages to terminate. When I solve the same set of ODE's in Octave, it 
almost immediately finishes. I prefer to use maxima however, so if anyone has 
a suggestion on how to increase performance I would be very grateful!

This is what I did in maxima:

==============================================
load("dynamics")

tau_m: 1.0
s_m: 1.0


eqm: s_m + f_1*mf_1 + f_2*mf_2 + f_3*mf_3 - m*(tau_m + (f_1 + f_2 + f_3)^2 + 
(f_1 - mf_1) + (f_2 - mf_2) + (f_3 - mf_3))$
eqf_1: -m*f_1 + (m + f_1)*mf_1$
eqf_2: -m*f_2 + (m + f_2)*mf_2$
eqf_3: -m*f_3 + (m + f_3)*mf_3$
eqmf_1: m*f_1 - (m + f_1)*mf_1 - mf_1*(f_2 + f_3) + f_1*( mf_2 + mf_3)$
eqmf_2: m*f_2 - (m + f_2)*mf_2 - mf_2*(f_1 + f_3) + f_2*( mf_1 + mf_3)$
eqmf_3: m*f_3 - (m + f_3)*mf_3 - mf_3*(f_2 + f_1) + f_3*( mf_2 + mf_1)$

msol: rk([eqm,eqf_1,eqf_2,eqf_3,eqmf_1,eqmf_2,eqmf_3],
[m,f_1,f_2,f_3,mf_1,mf_2,mf_3],[0.7,0.5,0.3,0.2,0.15,0.15,0.2],
[t,0,50,0.05])$
==============================================

and in octave:

==============================================
global tau_m = 1.0;
global s_m = 1.0;

function xdot = f (x, t)

global s_m;
global tau_m;

m = x(1);
f_1 = x(2);
f_2 = x(3);
f_3 = x(4);
mf_1 = x(5);
mf_2 = x(6);
mf_3 = x(7);


xdot(1) = s_m + f_1*mf_1 + f_2*mf_2 + f_3*mf_3 - m*(tau_m + (f_1 + f_2 + 
f_3)^2 + (f_1 - mf_1) + (f_2 - mf_2) + (f_3 - mf_3));
xdot(2) = -m*f_1 + (m + f_1)*mf_1;
xdot(3) = -m*f_2 + (m + f_2)*mf_2;
xdot(4) = -m*f_3 + (m + f_3)*mf_3;
xdot(5) = m*f_1 - (m + f_1)*mf_1 - mf_1*(f_2 + f_3) + f_1*( mf_2 + mf_3);
xdot(6) = m*f_2 - (m + f_2)*mf_2 - mf_2*(f_1 + f_3) + f_2*( mf_1 + mf_3);
xdot(7) = m*f_3 - (m + f_3)*mf_3 - mf_3*(f_2 + f_1) + f_3*( mf_2 + mf_1);

endfunction

x0 = [0.7; 0.5; 0.3; 0.2; 0.15; 0.15; 0.2];

t = linspace (0, 50, 1000)';		   

x = lsode("f", x0, t);
=============================================

thanks, Joachim.